feat(i18n): add Portuguese (Brazil) locale (pt-BR) (#6943)

Finalmente o idioma em Portugues do Brasil verá a luz do dia (se tudo
correr bem).

What has been done:

- Added pt-BR to .i18nrc.cjs and settings
- Included loaders in src/i18n.ts and apps/desktop-ui/src/i18n.ts
- Now Portuguese (BR) is displayed in the language selector
- Created empty main.json, commands.json, settings.json and
nodeDefs.json files to be populated by CI

- Checklist: the language appears in the dropdown list, selection occurs
without errors, the fallback to English, in case technical terms have no
translation, is working correctly.

- I will maintain the pt-br translation and review for as long as
necessary.

---------

Co-authored-by: Comfy Contributor <dev@example.com>

apps/desktop-ui/src/components/common/LanguageSelector.vue

@@ -59,7 +59,8 @@ const LOCALES = [
   ['fr', 'Français'],
   ['es', 'Español'],
   ['ar', 'عربي'],
-  ['tr', 'Türkçe']
+  ['tr', 'Türkçe'],
+  ['pt-BR', 'Português (BR)']
 ] as const satisfies ReadonlyArray<[string, string]>
 
 type SupportedLocale = (typeof LOCALES)[number][0]